The invention relates to a threaded tubular connection that can undergo plastic deformation by diametrical expansion and to the connection obtained after such expansion.
Threaded tubular connections are known that are formed between two great-length pipes or between a great-length pipe and a coupling and used in particular to produce casing strings or tubing strings for hydrocarbon wells or the like, such as those for geothermal wells.
Traditionally, wells are drilled with tools of different diameters, the top of the well being drilled using a large diameter tool, of the order of 500 mm, for example, while the well bottom is drilled at a smaller diameter, of the order of 150 mm. The wells are then cased using a plurality of concentric strings all suspended from the surface, pipes with the larger diameter extending from the surface to a depth of a few hundred meters and the smaller diameter pipes extending from the surface to the bottom of the well. The space between the casing pipes and the ground is generally cemented.
When the well is completely drilled and cased, a tubing string is lowered inside the smaller diameter casing string to allow hydrocarbons to rise to the surface.
Thus, fitting a well requires the use of a large number of pipes of different dimensions that are as thin as possible so as not to require too large a casing pipe diameter near the surface.
Taking into account the required mechanical characteristics, casing pipes and production pipes are generally produced from heat treated steel and are connected together by threaded connections, the thickness of the threaded connections being generally larger than that of the regular portion of the pipes and necessitating gaps in the diameters between the concentric strings.
API specification 5 CT from the American Petroleum Institute defines threaded tubular connections between great-length pipes (integral joint tubing, extreme line casing) and threaded and coupled connections comprising two threaded connections for connecting two great-length pipes using a coupling.
A number of patents have improved such connections and threaded connections: For example French patent FR 1 489 013, European patent EP 0 488 912 and U.S. Pat. No. 4,494,777 have aimed to produce threaded tubular connections known as xe2x80x9cpremiumxe2x80x9d connections with a particularly good seal thanks to metalxe2x80x94metal sealing surfaces and abutments between the male and female elements.
Very recently, new ways of using tubular strings in hydrocarbon wells have been considered, consisting of expanding the diameter of the pipes in the string by 10% to 20% using a mandrel forced through the inside of the column: see patents or patent applications: WO 93/25799, WO 98/00626, WO 99/06670, WO 99/35368, WO 00/61915, GB 2 344 606 and GB 2 348 657.
Such expansion can, for example, allow a casing string to be placed without having to cement the space between the external peripheral surface of the pipes and the surface of the hole drilled in the ground or lowering a string with a low bulk with respect to the hole.
Such expansion can also enable to plug holes in a casing or tubing pipe perforated by corrosion or by friction of the drilling strings, or to lower pipes with a low bulk which will be expanded to the desired diameter once in position.
However, the expansion technique can above all allow wells to be drilled that have a uniform diameter over their entire length and casing can be carried out using a string with a constant diameter, the pipes being introduced in the unexpanded state then expanded in situ to the diameter of the well.
It is then possible to substantially reduce the number of pipes required to fit a well by doing away with the largest diameter and thickest pipes, and thus reducing the cost of the well. It can even be thought of drilling a well directly with the casing string, which would then act as the drilling string.
However, prior art threaded tubular connections such as those described in U.S. Pat No. 4,494,777 do not allow such uses.
With such connections, after expansion:
an absence of a seal is observed which in particular prevents expansion from being carried out by hydraulically forcing the mandrel along the column;
sprue is observed from the male end towards the interior of the connection, which considerably and unacceptably reduces the operational internal diameter of the string by producing an internal projection into the space defined by the operational internal diameter;
possibly, the lip may be observed to break by exceeding the deformation capacity of certain particularly highly stressed zones due to variations in thickness along the male and female elements with respect to the thickness of the pipe body.
For this reason, the documents cited above dealing with expansion techniques only describe welded connections (coils of pipes previously butt-welded, deployed from the surface) or friction connections (xe2x80x9cslipsxe2x80x9d) as embodiments of the connections between the pipes, while threaded connections are known for their performance combining mechanical strength, a seal under all service conditions and the possibility of making a series of consecutive makeup-breakout trips.
It should be noted that U.S. Pat. No. 5,924,745 and WO 98/42947 describe threaded connections for connecting pipes known as xe2x80x9cESTxe2x80x9d pipes (expansible slotted tubing) provided with longitudinal slots allowing the pipes at the bottom of the hydrocarbon production wells to be expanded diametrically by passing an expansion mandrel through those pipes. Such threaded connections are not aimed at providing a seal, given that the pipes are provided with slots traversing the wall of the pipes and allowing a fluid that is outside the pipe (hydrocarbon from the field) to enter the pipe and rise to the surface therein.
We have thus sought to develop a threaded tubular connection that can resist the expansion operation in the well and which is tight to liquids and if possible to gases after said expansion operation.
We have also sought a simple, cheaply produced threaded tubular connection.
We have also sought a threaded connection with good metallurgical characteristics under operational conditions and thus, after expansion, with a sufficient yield strength in that condition, and free of brittleness and with good sulphide stress cracking characteristics.
In accordance with the present invention, the threaded tubular connection for expansion comprises a male threaded element with an external male threading at the end of a first pipe and a female threaded element with an internal female threading at the end of a second pipe.
Beyond the male threading and moving towards the free end of the element, the male threaded element comprises a male, non threaded lip with an external peripheral surface and terminates in a male end surface that is annular in shape and with a partially transverse orientation.
The female threaded element comprises a female threading that mates with the male threading and a non-threaded female housing for the male lip. This housing comprises an internal peripheral surface and a female shoulder surface that is annular in shape and with a partially transverse orientation connected to the internal peripheral surface of the second pipe.
The male threading is made up into the female threading to a position in which the surface of the male end is engaged against the surface of the female shoulder.
In accordance with a general characteristic of the invention rendering the threaded tubular connection capable of being sealed and of having a maximum internal cross section for passage after having undergone diametrical expansion in the plastic deformation region, the male end and female shoulder surfaces have complementary shapes producing, before expansion, embedding of the male end surface in that of the female shoulder.
Further, the external peripheral surface of the male lip is disposed with a small clearance from the internal peripheral surface of the female housing.
Embedding of the male end surface in that of the female shoulder means a bending moment on the free end of the male lip when the full thickness zone of the second pipe located beyond the female end is inclined with respect to the axis of the connection during expansion.
The embedding enables to constitute on the threaded connection, in the diametrically expanded condition, an annular sealing zone by metal/metal contact pressure between a portion of the external peripheral surface of the male lip and a corresponding portion of the internal peripheral surface of the female housing.
The embedding can also prevent any natural tendency of said free end to dip towards the interior of the string during expansion and produce an internal projection in the absence of such an embedding.
This behaviour during expansion, as established by the inventors in an unexpected manner, will be explained in the detailed portion of the description.
The term xe2x80x9csmall clearance between the external peripheral surface of the male lip and the internal peripheral surface of the female housingxe2x80x9d means clearances measured perpendicular to these surfaces of 0.3 mm or less.
The absence of substantial radial interference between the external peripheral surface of the male lip and the internal surface of the female housing due to this clearance means that these peripheral surfaces do not act as sealing surfaces in the non expanded connection. The inventors have established that a radial interference of these surfaces before expanding the threaded connection is not necessary for the production of a sealed connection after expansion.
They have also established that too much space between these surfaces does not allow them to interference fit after expansion, which interference fit is necessary to obtain a sealed threaded connection.
Prior art document U.S. Pat. No. 4,611,838 describes a threaded connection with a male lip in correspondence with a female housing and with an annular surface of the male end comprising an annular tooth and an annular surface of the female shoulder comprising an annular groove, abutting against each other, the male lip having a toroidal external peripheral end surface and the female housing having a tapered internal peripheral surface.
Those peripheral surfaces radially interfere at the end of makeup to constitute sealing surfaces; U.S. Pat. No. 4,611,838 aims to maximise the radial interference of the external toroidal peripheral surface of the male lip with the internal tapered peripheral surface of the female housing at the end of makeup (and thus provide the seal for the threaded connection) thanks to the shape of those peripheral surfaces and the supporting effect of the lower surface of the groove for the lower surface of the tooth.
However, the male end surface in that patent is not completely embedded in that of the female shoulder of the threaded connection and thus cannot transmit a bending moment to the free end of the male lip because of the free space between the upper wall of the tongue at the free end thereof and the upper wall of the groove at the base thereof.
There is no suggestion in that document regarding the effects on the sealing surfaces of diametrical expansion with plastic deformation, nor that the threaded connection could successfully undergo such expansion. In the inventors"" experience, the seal of a threaded connection in accordance with U.S. Pat. No. 4,611,838 could not be ensured after such an expansion.
U.S. Pat. No. 3,870,351 describes a configuration of the male lip and male end and female housing close to the configuration of U.S. Pat. No. 4,611,838, the surface of the free male end being convexly bowed and bearing against a concavely bowed female shoulder surface to produce two sets of metalxe2x80x94metal sealing surfaces, one at the level of the bowed surfaces, the other at the external peripheral surface of the male lip and on the internal peripheral surface of the female housing. Such a configuration can increase the radial interference between the peripheral sealing surfaces.
International patent application WO 99/08034 describes a threaded connection with square threads with a male lip corresponding with a female housing and with annular male end surfaces and female shoulder surfaces in the form of rabbets that come into abutment and embed into each other. The external peripheral surface of the male lip and the internal peripheral surface of the female housing have cylindrical portions that radially interfere with each other to form a set of peripheral sealing surfaces at the end of makeup when the male and female rabbets are embedded.
Finally, U.S. Pat. No. 6,047,997 describes a drilling string structure for underground ducts for which there is no particular demand for a seal. The male end surface in that patent is embedded in a female shoulder surface but the figures show a large space between the external peripheral surface of the male lip and the internal peripheral surface of the female housing.
None of these four cited documents describes a structure that is identical to that claimed in the present invention. Further, none of them considers diametrical expansion of threaded connections and nor do they describe the possibility of producing sealed threaded connections after such expansion.
Preferably, in accordance with the present invention, to enable it to be embedded in the female shoulder, the male end surface has the form of a rabbet constituted by a transverse surface on the side directed towards the interior of the threaded connection and an axially projecting annular tongue on the opposite side. In order to co-operate with the male end surface, the female shoulder surface has the form of a rabbet constituted by a transverse surface on the side directed towards the interior of the threaded connection and an annular groove on the opposite side, the transverse surface of the male rabbet co-operating with that of the female rabbet and the annular tongue co-operating with the annular groove.
Highly preferably in the present invention, the annular walls of the groove interference fit with those of the tongue.
Advantageously, in the made up position, the transverse surfaces of the rabbet on the internal side thereof abut each other. Alternatively, they can be simply in quasi-contact.
Preferably again, the radial thickness of the tongue on the male rabbet is substantially equal to that of the transverse surface of the same rabbet.
Preferably again, the axial height of the tongue of the male rabbet is substantially equal to its radial thickness.
Preferably again, the external peripheral surface of the male lip and the internal peripheral surface of the female housing are cylindrical surfaces: machining these non-interfering surfaces is thus particularly simple and cheap.
Advantageously, the thickness of the male lip is in the range ⅓ to ⅔ of the thickness of the first pipe.
This range of thickness of the male lip ensures a critical cross section at the base of the threading that is sufficient to provide adequate strength on axial tension of the threaded connection.
Advantageously again, the ratio between the length and thickness of the male lip is in the range 1 to 4, the length of the male lip being measured from the transverse surface of the male rabbet.
The minimum value of this ratio allows plastic deformation of the male lip and of the female housing during expansion; these plastic deformations generate surfaces bearing against each other with a high contact pressure and thus provides the seal for the threaded connection after expansion.
The maximum value of this ratio enables to avoid uncontrolled buckling of the male lip, which buckling would result in said lip projecting inside the pipe string.
Highly advantageously, the male threaded element has a groove at the end of the threading between the threading and the male lip. This groove facilitates plastic deformation of the male lip during expansion of the threaded connection.
Preferably, the depth of the groove is substantially equal to the height of the male thread such that the base of the male threads opens into the base of the groove.
Preferably again, the length of the groove is in the range 2 to 8 times its depth. A length/depth ratio of less than 2 will not allow the groove to facilitate plastic deformation of the lip. A length/depth ratio of more than 8 will result in a high risk of buckling of the material towards the interior of the column during expansion.
The invention can advantageously be applied both to threaded connections with tapered threadings and to threaded connections with straight threadings with single and/or multiple stages.
Advantageously again, the first pipe and the second pipe have the same internal diameter both at the level of the threaded elements and at the level of the pipe body, facilitating expansion operations.
Advantageously again, this is the same for the external diameters.
Highly advantageously, the threaded connection is integral in nature, i.e., each pipe is a great-length pipe which comprises a male threaded element at one end and a female threaded element at the other end, the male element of one pipe being made up into the female element of another pipe and so on to constitute a string.
The aim of the present invention is to protect a sealed threaded connection resulting from diametrical expansion in the plastic deformation region of a threaded connection as defined above.
Preferably, the diametrical expansion that is carried out is more than 10%.
The present invention also aims to protect the threaded connections described above in the non expanded or expanded condition wherein the threaded elements are produced from steel comprising nitrogen fixing elements rendering the steel insensitive to ageing by work hardening. The steel is also heat treated to maximise its uniform elongation properties. This results in good properties in service.
The present invention also aims to protect a process for producing a sealed threaded tubular connection.
In accordance with this process, starting from a threaded tubular connection of the invention as described above, termed the xe2x80x9cinitial threaded tubular connectionxe2x80x9d for which no sealing properties are required, this initial threaded connection undergoes diametrical expansion in the plastic deformation region using an expansion mandrel with a diameter that is higher than the internal diameter of the pipes of the initial threaded connection, the expansion mandrel being axially displaced in the initial threaded connection. The dimensions of the male lip and the female housing are such that during passage of the mandrel, the male lip and the female housing together first undergo plastic bending deformation while only the female housing then undergoes plastic deformation in the reverse, straightening, direction, which finally interference fits the male lip with the female housing.
Preferably, bending of the male lip is delimited by the presence of a groove at the end of the male lip on the male threading side.
Preferably again, the threaded tubular connection employed is integral in nature and the expansion mandrel is displaced from the male threaded element towards the female threaded element.